Use the correct article (a or an):
... academy, ... album, ... bright album, ... actor, ... great actress, ... arch, ... marble arch,
... chance, ... unlucky chance, ... dove, ... ear, ... elf, ... tiny elf, ... horse, ... hour, ... long
hour, ... institute, ... lemon, ... mill, ... obelisk, ... opera, ... Italian opera, ... owl, ... paper, ...
rabbit, ... quarter, ... train, ... wing, ... voyage, ... year.

Ответ:

An academy, an album, a bright album, an actor, a great actress, an arch, a marble arch,  a chance, an unlucky chance, a dove, an ear, an elf, a tiny elf, a horse, an hour, a long  hour, an institute, a lemon, a mill, an obelisk, an opera, an Italian opera, an owl, a paper, a rabbit, a quarter, a train, a wing, a voyage, a year.

Если слово начинается с согласной, то просто артикль а. Если с гласной, то an.

an hour - исключение